Case hardened isn't really a spec so it's not clear what you really need but McMaster-Carr has grade 8 strenght studs that match your needed dimensions.
May I ask why you feel that case hardened studs are needed? Case hardening is for abrasive wear and doesn't improve the other mechanical properties as it's a surface treatment of the material that doesn't go very deep. If you do need something that resists abrasive wear there's other choices that might suit your application. What are you wanting to use the studs for?
Case hardened isn't really a spec so it's not clear what you really need but McMaster-Carr has grade 8 strenght studs that match your needed dimensions.